Today, “Voice over Internet Protocol (VoIP)”, also referred to as IP telephony, is adopted for voice communications over an Ethernet local area network (LAN). Compared to operating two separate communication networks, e.g. an Ethernet LAN for data communications and a PBX system for voice communications in an office communication environment, a converged system by applying an Ethernet LAN for both data and voice communications would be highly desirable for saving costs in deploying and operating the converged network infrastructure as well as for providing more tightly integrated data and voice applications.
Nevertheless, there are still technical and operational difficulties and limitations for such implementations because voice and data communications place very different requirements on the network performance. The Ethernet LAN implements a native “best-efforts” technology that was originally designed only for data transmission among computers. For this reason, the Ethernet networking technology in its primitive form does not provide any Qualify of Service (QoS) necessary for voice communications in terms of transmission bandwidth, packet delay, jittering, packet loss and etc. Furthermore, an Ethernet LAN inherently tends to be less reliable and secured than a traditional PBX telephone system does.
For better understanding of the background of this invention, general developments and current applications of Ethernet technology are first discussed.
Ethernet is a computer networking technology that was initially developed in 1970s as a local area networking solution for data communications among data terminal or host devices such as computers, printers, servers and etc within a local area such as an office building. Because of its simplicity and scalability, Ethernet has become the most widely adopted LAN technology and was standardized by IEEE (The Institute of Electrical and Electronics Engineers) as IEEE Standard 802.3, “Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications”.
According to IEEE Standard 802.3, a cable of four twisted pairs, referred to as a LAN cable hereinafter, such as Category 5 cable or the like is used to provide a full-duplex communication link between a network device such as an Ethernet switch and terminal device such as a computer. Typically, the four twisted pairs of the LAN cable are referred to as pair 1-2, pair 3-6, pair 4-5; pair 7-8. A standard 8-conductor RJ45 plug assembled with the LAN cable is usually used for connecting with a standard 8-conductor RJ45 jack. Of variants of Ethernet protocols, 10Base-T and 100Base-TX, referred to as 10/100Base-T hereinafter, refers to transmission of Ethernet data signals at 10 Mbps (bit per second) and 100 Mbps respectively by using pair 1-2 and pair 3-6 of the LAN cable while pair 4-5 and pair 7-8 of the LAN cable are left unused. 1000Base-T refers to transmission of Ethernet data signals at 1000 Mbps by using all the four pairs of the LAN cable.
An Ethernet LAN in the early days was usually found in a shared bus topology by which multiple computers were physically hooked up to a single cable segment, sending and receiving packets to each other based on the communication protocol called “Carrier Sense Multiple Access with Collision Detection (CSMA/CD)” as specified in IEEE Standard 802.3. Today, Ethernet switches are typically used for achieving much higher data throughput with improved network reliability. An Ethernet Switch is a multi-port LAN interconnection device which operates at the data link layer (layer 2) of the network hierarchy (OSI reference model). It allows simultaneous packet communications among multiple pairs or groups of computers.
For the purpose of remotely providing power to terminal devices such as IP phones, the technology of “Power over Ethernet (PoE)” has been developed that enables a unified supply of data and power through a single access point by sending power over a LAN cable. The PoE technology eliminates the need for a separate power cabling and installations of bulky AC adapters and AC outlets. As a matter of fact, such a technology has been standardized as an IEEE standard, referred to as IEEE Standard 802.3af.
According to IEEE Standard 802.3af, a Power Sourcing Equipment (PSE) operating as either a Midspan or Endpoint apparatus provides DC or low frequency inline power over two pairs of a LAN cable to a remote terminal device in one of two modes, referred to as “Alternative A” and “Alternative B”. In “Alternative A”, pair 1-2 and pair 3-6 of the LAN cable are used as two conducting paths for transmitting inline power as a common mode voltage. Because pair 1-2 and pair 3-6 of the LAN cable are also used for transmitting 10/100Base-T data signals in differential mode, “Alternative A” allows transmission of both power and data signal over the same two twisted pairs. Therefore, “Alternative A” is applicable to both 10/100Base-T and 1000Base-T. In “Alternative B”, pair 4-5 and pair 7-8 are solely used as two conducting paths for transmitting inline power as a common mode voltage. Therefore, “Alternative B” is applicable only to 10/100Base-T. According to IEEE Standard 802.3af, a PoE enabled powered device (PD) such as an PoE enabled IP phone shall be able to support both “Alternative A” and “Alternative B”. In “Alternative A”, the voltage polarity of inline power received by a PD depends on the type of the LAN cable being used which is either a straight-through cable or cross-over cable.
Technically, an IP phone digitizes a channel of analog voice signal, encapsulates the digitized voice signal into a sequence of IP packets that are further carried by Ethernet packets, and the Ethernet packets are sent over an Ethernet LAN to another IP phone. For achieving satisfactory voice quality, the Ethernet LAN is required to be capable of providing adequate QoS.
Two existing Ethernet LAN techniques have been developed for providing QoS and segmenting data traffic within an Ethernet switch which can be utilized to improve the performance of IP telephony communications over an Ethernet LAN. One technique is to prioritize packets inside an Ethernet switch so that packets with higher priority are transferred or forwarded with reduced amounts of packet delay, packet jitter and packet loss. The other technique is to use virtual LAN (VLAN) technique to logically separate data traffic at the data link layer running inside an Ethernet switch so as to provide a higher level of security as well as a more manageable and better guarded bandwidth among various types of data traffic. As a matter of fact, these two techniques of packet prioritization and virtual LAN (VLAN) for switching Ethernet packets have been standardized as an IEEE standard, referred to as IEEE Standard 802.1p/Q.
Although Ethernet switches that are built with the packet prioritization and VLAN mechanism can be used to implement an Ethernet LAN for better supporting IP telephony communications, there are still several technical and operational issues that may impede the wide adoption of this technology. Some of these technical issues are described below.                1) System reliability issue. Running data and voice communications over a single Ethernet LAN is like “putting two eggs into one basket”. Once the LAN crashes or becomes paralyzed by malicious attacks of denial of services (DOS), both data and voice communications are lost at the same time.        2) Security issue. Although a VLAN can separate voice traffic from other traffic in a network for implementing a more secured IP telephony system over an LAN, security is still a concern because the VLAN only logically separates voice traffic from other traffic at the data link layer and there are still chances that such a VLAN maybe compromised and voice packets maybe intercepted and eavesdropped.        3) Network upgrade issue. To upgrade an old Ethernet LAN for IP telephony communications, all the legacy Ethernet switches may have to be replaced with new Ethernet switches that are built with the packet prioritization and VLAN capabilities. Such a forklift network upgrade is not only costly but also is likely to cause disruptions to the normal operation of the network before the network becomes stabilized.        4) Network management and maintenance issue. Migrating a legacy Ethernet LAN to a new LAN for IP telephony communications also introduces extra amount of workloads and costs in setting up and managing the new network. The network setup and management become much more complicated and time consuming due to the fact that a lot more items and parameters related to the network behaviors and performances have to be configured and monitored, most of times manually by well trained and experienced IT professionals. The complexities and the need of highly trained IT personnel for setting up and managing an Ethernet LAN for IP telephony communications introduce hidden costs to the ownership of the overall network system.        5) Emergence 911 calls issue. In a traditional PBX system, a telephone is connected to a PBX port/line that is assigned with a fixed telephone number. This unique 1-to-1 mapping between a telephone number and a phone line or PBX port is used to track the physical location of the telephone. However, in an IP telephony system, the phone number of an IP phone is not associated with the port of an Ethernet LAN switch to which the IP phone is connected to. Instead the phone number is assigned based on the MAC (Media Access Control) address of the IP phone itself. MAC address is a physical address for identifying a device connected to a network. In other words, an IP phone can be connected to a different port of the LAN switch but still has the same telephone number. Such mobility nature of IP phones makes it difficult in tacking the location of the IP phone to support emergency E-911 calling in an IP telephony system.        
Meanwhile, because of the benefits of the convergence of data and voice communications over an Ethernet LAN, there are demands to resolve these technical and operational limitations that may hinder the broad applications and deployments of IP telephony communications over Ethernet LANs.